Direct seeding of rice has become a main planting method due to the low labor input and high economic benefit in South China.  Dry direct seeding (DDS) has been widely used for single-season rice planting establishment.  However, few studies have examined the performance of early-season indica rice under mechanical dry direct seeding.  A two-year field experiment was conducted with two indica rice cultivars (i.e., Zhongjiazao 17 and Zhuliangyou 819) to study lodging characteristics and grain yield formation under DDS, flooded direct seeding (FDS) and wet direct seeding (WDS) patterns.  The results showed that the annual grain yield in DDS was higher by 14.42–26.34% for cultivar ZLY819 and 6.64–24.58% for cultivar ZJZ17 than in WDS and FDS, respectively, and these increases were mainly attributed to the improvement of the panicles.  The DDS pattern significantly increased the seedling emergence rate of early indica rice cultivars, and increased total dry weight and crop growth rate.  Meanwhile, shorter basal internodes, better stem diameter and stem wall thickness and lower lodging index were found in DDS in contrast to FDS and WDS.  In particular, DDS improved the stem lodging resistance.  Our results suggested that the appropriate direct seeding method was beneficial for improving the grain yield and lodging resistance of early indica rice.

Length of grain affects the appearance, quality, and yield of rice.  A rice long-grain chromosome segment substitution line Z744, with Nipponbare as the recipient parent and Xihui 18 as the donor parent, was identified.  Z744 contains a total of six substitution segments distributed on chromosomes (Chrs.) 1, 2, 6, 7, and 12, with an average substitution length of 2.72 Mb.  The grain length, ratio of length to width, and 1 000-grain weight of Z744 were significantly higher than those in Nipponbare.  The plant height, panicle number, and seed-set ratio in Z744 were significantly lower than those in Nipponbare, but they were still 78.7 cm, 13.5 per plant, and 86.49%, respectively.  Furthermore, eight QTLs of different traits were identified in the secondary F₂ population, constructed by Nipponbare and Z744 hybridization.  The grain weight of Z744 was controlled by two synergistic QTLs (qGWT1 and qGWT7) and two subtractive QTLs (qGWT2 and qGWT6), respectively.  The increase in the grain weight of Z744 was caused mainly by the increase in grain length.  Two QTLs were detected, qGL1 and qGL7-3, which accounted for 25.54 and 15.58% of phenotypic variation, respectively.  A Chi-square test showed that the long-grain number and the short-grain number were in accordance with the 3:1 separation ratio, which indicates that the long grain is dominant over the short-grain and Z744 was controlled mainly by the principal effect qGL1.  These results offered a good basis for further fine mapping of qGL1 and further dissection of other QTLs into single-segment substitution lines.